Circuit for electrical discharge apparatus



oct. 11, 1932. C R, KEITH 1,881,657

CIRCUIT FOR ELECTRICALv DISCHARGE APPARATUS Filed March 24, 1928v A afm/fr Y Patented Oct. 11, 1932 'STATES PATENT OFFICEl on'rnii R. KEITH, OE EAST ORANGE, vNEW JERSEY, AssIGNOR To lREEL TELEPHONE 'LAPoR-ATORIES, INCORPORATED, OE NEW YORK, N. Y., A CORPORATION OF NEW YORK f CIRCUIT POR ELECTRICAL DISCHARGE APPARATUS Application ined maren 24, 192s. serial No. 264,496.

This invention relates'to circuits for eloctric discharge apparatus and particularly to circuits for electric discharge apparatus khavingnegative resistance characteristics.

An object of the invention is to make the input resistance of a space discharge device Vinfinite or of ahigh value for impressed waves of a wide range of frequencies.

, A second object is to make the input impedance of ay space discharge device high for impressed waves of a single frequency or a band of frequencies.

y related object is to secure in an electric discharge amplifying device an increased degree of amplification as a result of improvement in the input impedance characteristics of the amplifying device.

It is well knownk that when an incompletely evacuated space discharge device of the three-electrode type, or such a device containing a small quantity of an inert gas, is

operated, the ionization'of some yof the particles of gasbetween the anode and the control electrode inthe device-may produce an effective 'negative resistance between the cathode and the control electrode of the de- Y v vice for impressed waves of alternating current. Y

In accordance with the present invention thisnegative resistance to alternatingV currents in the input circuit of a gaseous threeelectrode space discharge device is utilized in making the total input impedance of the device very high for impressed waves of predetermined frequencies,' and thus to greatly increase'the amplifying power of the device for these frequencies. This is accomplished invpart by connecting between the cathode and control electrode of the space discharge 40 device effectively in shunt to the negative resistance pat-h in the input circuit of the device a positive resistance substantially equal in value. to this negative alternating current resistance which has the effect of making the net resistance component of the input impedance of the device infinite, or very large,ffor impressed waves of a wide range of frequencies.

l The effect of the resistance component of the input impedance having been thus neutralized, the effect of the reactance component of the input impedance of the'device due to the natural capacity between the cathode and control electrode of the device may be effectively annulled by combining with this natural capacity, reactance in the input circuit of the device to forma timed circuit or filter of suoli impedance characteristics as to make the total input impedance of the device very high for waves of a single frequency or a band of frequencies. The reactances and resistances forming the tuned circuit or lter, or a portion thereof, may be provided by separate resistance and inductance elements or by utilizing the-leakage,

inductance, distributed winding capacity and resistance of a transformer coupling an 'incoming signal line or circuit to the input circuit of the space discharge device.

The invention itself and its objects and advantages will be best understoodby reference,

to the following description taken in connection with the accompanying drawing l in which: I

Fig. l shows in schematic form the invention embodied in an amplifier circuit; and

Figs. 2 and 3 show modifications of a portion of the circuit of Fig. l which may be utilized to obtain different advantageous rcsults which will be pointed out in connection with the description of the figures.v

In Fig. l is shown an amplier circuit A constructed in accordance with the invention connected between an incoming circuit l and an outgoing circuit 2. Included in the amplifier circuit A is a three-electrode space discharge amplifying device comprising an envelope 3 enclosing the usual electrodes7 a cathode or lament 4, an anode or plate 5 and a grid or control electrode 6. Heating current for the cathode 4 is supplied by a filament battery 7. c Space current for the tube is supplied by a source of voltage 8, and negative polarizing potential for the grid 6 by the grid battery 9.

The incoming circuiti is effectively connected between the cathode 4 and control electrode 6 of the amplifying tube by yinput transformer 10, and the outgoing circuit 2 is effectively connected between the anode 5 and the cathode l'by the output transformer 11. In thel input circuit of the amplifier be# f twee'nthe input transforinei` 10 and the input Y 4element 12 andan inductance element. 13 inV Y the space path is given by the reciprocal ofv the slope ofthe grid current curve',`and may be made very high, positivey or negative, de`

vand the gridy potential. 4 In the embodiment of the invention being described, the tubeB and its associated cirv'electrodes '-l and 6 of the amplifying tube 8 is connected an impedance network N, which, in the particular modifica-tionjof. the .invention shown in' Fig. 1,1 .comprises a resistance 1 sure in thev envelope'is preferably of the order 20 of about'lO-3 mm. of mercury. Such; a de* vice may be made to offer an e'ective negative vresistance to alternating currents im# pressed on the grid circuit of the device, the value of vwhich resistance is substantially in-v dependent of capacity coupling effects between the electrodes and the nature of the eir-V ternal circuitsc'oupl-ed toV the device. rfl'iis effective negative resistance, which'in the circuitsof Figs. 1,2 and Slis indicated by the dotted resistance element designated-#R between the grid 6 and cathode 5', is produced by the ionization of some of the gas particles in thepath between the anode 5 and grid 6 of the tubeby the electron currentto the anode 5. If the vgrid isnegatively polarized, the positive ions are attracted tothe 'grid 6 causing al current to flow in they grid circuit.v yWhen the gridvoltage ismade more nega- Ative the plate current is decreased sothat kfewer positive ions are produced in the-space VVpath and thegrid` current is reduced. In

other-words', the grid-curre'nt'has a negative slope. The alternating current resistance of pending on the value of the plate current cuits 'are so designed that the negative resistance effect in ythe grid circuit of the tube for impressed alternating current` waves isY obb tained at the operating'point ofthe tube. YThis negative resistance effect isgutilized in accordance withl the invention for obtaining avery high infinite input resistance for thel tube over a wide range `offiinpress-edI fre-A .I quencies by making-,the net resistance yeec-y tively in shunt to t-he'negative A.. G. resist-V ancev `-R, including 4the resistance element 12, Vof substantially ythe same value as the* negative A. G. resistance.

'the tubev 3 Vhasv enough inter-electrodeV capacity it may be necessary in order to'A makey the effective input impedance infinite or very high for waves ofa particular frequency impressed on its input circuit through input transformer 10, tolneutralize the effect of the input reactance of the tube 3 due, for exampldto lthe naturalcapacity between the grid 6 and the vcathode Ll, whichnatural capacity is indicated in Figs. 1, 2 and 3Y by the dotted condenser designated Ggf, at that fi-e'- quency. This'isaccomplished in accordance with thek inventioir'by making `theeirternal inductance effectively in shunt to thecapacity Ggf', including the inductive element 13, of such value asto resonate with the capacity Ggf at thedesired frequency to' be amplified.

rlhe effects of the resistance component and reactance component o f theinput impedance ofthe amplifier A having been controlled by proportioning the external resistance and re-Y active elements ofthe input circuit ofntube 'i 3 with respect to the internal characteristics of the tube vin the manner pointed out above, itis apparent that the resistance component of the input impedance of the amplifying device?) will be substantially infinite fory all frequencies Vimpressed thereon from the inconiing line 1 and the. total input impedance of the device'will be very highor infinite for impressed alternating current waves of substantially theresonant frequency of the network N in conjunction with the input capacity of the tube. Incoming waves of the resonant frequency from incoming circuit 1 impressed on the input circuit of amplifier will, therefore, receive greatly increasedr am? plification therein over that of waves of other frequencies. In other words, the amplifier A acts as a very highly selective amplifying cir cuit for waves of the particular resonant frequency. n

The amplifier circuit of the inventionhas another important, advantage in that the input impedance of the amplifier being very high orinfinite, the incoming line 1 connected to the input circuit thereof may be terminated A in a definite impedance, as this terminating impedance is substantially independent of 'normal changes in the input impedance of the' amplifier. l Y y ln Figs. 2and 3 arey shown alternative networks which may be utilized inpla'ce of the resonant circuit type o-f network shown in the circuit of Fig. 1. y f

The network Nfofv Fig.f2 differs from that of Fig. .1 in that it comprises a vseries inductance 14 instead of the shunt inductance 18 of Fig. 1. The inductance'14 in conjunction with the grid to cathode natural capacity Ggf of 'the amplifier tube andthe other rc actance in the input circuit thereof will forniL a filter of the low pass type, having a. cut-ofi' as determined by the relative valuesV of the reactances therein. Such a network when used in the circuitl offFig. 1 will transmit eciently tol-the amplifyingv tube 3 Ywaves i impressed thereon from the incoming line 1 of all frequencies below the cut-oli' frequency of the `filter and will substantially attenuate .all frequencies in the impressed waves above the amplifier circuit will give greatly increased amplificationfor this band of frequencies over that of impressed frequencies outside the band.

' .Y The networkwN of Fig. 3 differs from that of Fig. 1 in that it comprises in addition vto the shunt resistance and shunt inductance element of the latter figure, a series inductance element and a series condenser element. This combination, when used in the circuit of Fig. 1 in place of the resonant circuit network there shown, will form with the natural capacity betweenth'e cathodeand grid, Ggf, of the -amplifying tube, a filter of the band vpass type having upper and lower cut-off frequencies determined by the relative values .of the inductive and capacitive elements in the circuit. 4 This band pass filter will transmit efiiciently to the amplifier tube 3 all waves from the incoming line 1 having frequencies Y within the limits'as determined by the cut-off frequencies of the filter and will greatly attentuate all frequencies in the received waves outside these limits. The input impedance of the amplifier A using the band pass type of net work of Fig. 3 will be very high for all impressed frequencies Within the band limits,

and theamplifier, therefore will selectively amplify in a high degree the selected frequencies for transmission over the outgoing line 2.

Reference is made to Campbell Patents 1,227,113 and 1,227 ,114, issued May 22, 1917, for detailsv as to the theory and operation of the filters of the type illustrated in Figs. 2

and 3 of the drawing,

As the gas pressure in the usual commercial gaseous tubes are subject to variations due to temperature changes, etc., Within the tube, and the value of the effective negative A. C. resistance in such tubes being dependent on gas ionization will vary with changes in gas pressure therein, it may be desirable in order to make the device of the invention more `stable to utilize some means therewith for maintaining constant the gas pressure within the tube. Any one of the various methods which have been proposed in the prior art for this purpose may be used. For example, the pressure control means disclosed in Van der Bijl Patent 1,495,279, isued May 27, 1924 will be satisfactory for this purpose.

It is to be understood that the networks illustrated in Figs. 1, 2 and 3 of the drawing are merely typical examples of networks which may be used for accomplishing the purpose of the invention, and that any other suitable type of resonant circuit, low pass filter, high pass filter'or band pass'iilter may be'used instead in accordance withithe invention. f

It. is to be yunderstood also' that, valthough to facilitate thedesc'ription ofthe invention, separatevresistance, inductance and condenser eiements have been shown as making up the network Nin the various modifications of the amplifier circuit of the invention, to accomplish the results as pointed out, the resistance,

`lealage inductance or distributedy capacity of the inputtransformer 10 or other coupling'device between the incoming line and the amplifier circuit may be utilized to perform part or all of the functions of the separate elements shown. f

The system above illustrated anddescribed should be considered merely as typical and not as-limiting the invention, the ,scope of which is defined in the appended claims.

lVhat is claimed is:

1. In combination, a gas-filled electric space discharge device having an input circuit, a cathode and a control electrode, and operating through the effect of ygas ionization to produce an effective negative resistance between said cathode and said control electrode for impressed waves of alternating current, and means for making the net input resistance of said device substantially infinite for impressed waves of a Wide range of frequencies comprising means having an electrical resistance substantially equal in value to said negative resistance, connected in said input circuit betweensaid cathode and said control electrode. 2. In combination, a gas-filled space discharge devicel having an input circuit, a cathode and a control electrode, and operating through thereflect of gas ionization to produce an effective negative resistance between said cathode and said control electrode for impressed waves of alternating current, and means for making the net input impedance of said device substantially infinite for impressed alternating current waves of a certain frequency range, said means comprising means having an electrical resistance substantially equal in value to said negative resistance, connected in said input circuit between said cathode and said control electrode, and means connected between said cathode and said control electrode and having such a value of reactance as to neutralize substantiallyin said input circuit t-he effect of the input capacity of said device for impressed waves of said frequency range.

3. In combination, a space discharge amplifying device containing an inert gas to a pressure in the order of about 10'3 mm. of mercury and having an input circuit, a cathode and a control electrode, and operating through the effect of gas ionization to give an effective negative resistance between said cathode and said control electrode for im- Yteristicsof said deviceover a range-offre# Y pressed waves of alternating current, and I 'Y means to improve vthe amplification charac-VK quencies icomp'rising means having an! electrical resistance substantially equal'. in value tosaid negative resistance, connected in saidA -1 input circuit between-'said cathodeand said control electrode, and means connected in saidv input circuit between said cathode vand,

Vsaid controll electrode and having such a value of inductance as to'forin with .the input capacity of said device a tuned "circuit reso-v nant at a frequency near the iniddle ofv said range.' f w I 4. 'In combination, a space dischaiyge,am-` plifyingdevice containinga-n inert gas to a ypressure in the order of about 10'3 mm. of

mercury, and having an input circuit, a cathode and a control electrode, said device operating throughthe efect of gas ionization to produce an effective negative resistance between'said cathode and control electrode for impressed waves of alternating current, and

means lto improve the amplification characteristics of said device ,over a givenrange of frequencies, said means comprising means having an electrical resistance substantially equaling in Value said nega-tive resistance, connected between said cathode and said 'con'- trol electrode in said input circuit, and reactive elements connected inv said input circuit between said cathode and said control electrode and havingsuch values as to form Y with'said resistance and theinput capacity of said devicea filter offering a'high imgivenv range. d

pedance to waves of frequencies within said In' witness whereof, I hereunto sub-scribe ,i my naine this 22 dayof March, 1928. V

` ,A 7 CLYDE R. KEITH.. 

